This invention relates to a novel class of fluorovinyl ether monomers which are useful as cure site monomers in fluoroelastomers, a process for the preparation of these fluorovinyl ether monomers and to curable fluoroelastomer copolymers having copolymerized units of these fluorovinyl ether monomers.
Elastomeric fluoropolymers (i.e. fluoroelastomers) exhibit excellent resistance to the effects of heat, weather, oil, solvents and chemicals. Such materials are commercially available and are most commonly either dipolymers of vinylidene fluoride (VF2) with hexafluoropropylene (HFP) or terpolymers of VF2, HFP, and tetrafluoroethylene (TFE). While these di- and terpolymers have many desirable properties, including low compression set and excellent processability, their low temperature flexibility is not adequate for all applications, nor is their resistance to attack by alkaline solvents.
It is known that incorporation of perfluorinated ether monomer units into vinylidene fluoride elastomers improves low temperature properties, i.e. cured articles made from these polymers seal well at low temperatures. For example, Carlson, in U.S. Pat. No. 5,214,106 discloses that when perfluoro(methyl vinyl) ether (PMVE) is substituted for HFP, the resultant VF2/PMVE/TFE copolymers have glass transition temperature (Tg) values which are 10xc2x0-20xc2x0 C. lower than those of the corresponding VF2/HFP/TFE copolymers. Tg is often used as an indicator of low temperature flexibility because polymers having low glass transition temperatures maintain elastomeric properties at low temperatures.
Other common fluoroelastomers include the copolymers of TFE with one or more hydrocarbon olefins such as ethylene or propylene, and, optionally VF2 (for example U.S. Pat. No. 4,758,618). These copolymers are generally more resistant to attack by alkaline solutions than other types of fluoroelastomers. The copolymers may also contain a perfluoro(alkyl vinyl) ether (PAVE) in order to impart good low temperature scaling properties (U.S. Pat. No. 4,694,045).
Many of the fluoroelastomers listed above require incorporation of a cure site monomer into their polymer chains in order to crosslink efficiently. Without such a cure site monomer, the fluoroelastomer may not react at all with curing agents, it may only partially react, or reaction may be too slow for use on a commercial scale. Seals made from poorly crosslinked elastomers often fail sooner than might otherwise be expected. Unfortunately, disadvantages are associated with many of the cure site monomers in use today. For example, monomers which contain reactive bromine or iodine atoms can release byproducts during the curing reaction that are harmful to the environment. Other cure site monomers (e.g. those which contain double bonds at both ends of the molecule) may be so reactive that they disrupt polymerization of the fluoroelastomer by altering the polymerization rate, terminating polymerization, or by causing undesirable chain branching, or even gelation to occur. Lastly, incorporation of a cure site monomer into a fluoroelastomer polymer chain may negatively impact the properties of the fluoroelastomer (both physical properties and chemical resistance).
There thus exists a need in the art for cure site monomers which are environmentally friendly, do not disrupt polymerization and which do not detract from the properties of the fluoroelastomer.
The present invention is directed to a fluorovinyl ether monomer of the formula CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFxe2x95x90CF2, wherein Rf is a C1-C8 perfluoroalkyl group or a C1-C8 perfluoroalkoxy group, n is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1 to 4.
The present invention is also directed to a process for the preparation of the above fluorovinyl ether. The process comprises the steps of
A. chlorinating an hydroxy vinyl ether compound of the formula HOxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFxe2x95x90CF2 to produce a chlorinated hydroxy ether of the formula HOxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFClxe2x80x94CF2Cl;
B. condensing said chlorinated hydroxy ether with hexafluoropropene to produce a chorinated ether of the formula CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFClxe2x80x94CF2Cl; and
C. dechlorinating said chlorinated ether to produce a fluorinated vinyl ether of the formula CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFxe2x95x90CF2.
The present invention is also directed to a fluoroelastomer composition comprising
A. copolymerized units of a first monomer, said first monomer being a fluoroolefin selected from the group consisting of vinylidene fluoride and tetrafluoroethylene;
B. copolymerized units of a second monomer, different from said first monomer, said second monomer selected from the group consisting of i) fluoroolefins, ii) hydrocarbon olefins, iii) perfluoro(alkyl vinyl)ethers and iv) perfluoro(alkoxy vinyl) ethers, and
C. copolymerized units of a fluorinated vinyl ether cure site monomer of the formula CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFxe2x95x90CF2, wherein Rf is a C1-C8 perfluoroalkyl group or a C1-C8 perfluoroalkoxy (group, n is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1 to 4.
The present invention is also directed to a polyhydroxylic curable composition of the above fluoroelastomer.
The fluoroelastomers utilized in the curable compositions of the present invention are copolymers capable of undergoing crosslinking reactions with polyhydroxylic compounds to form cured elastomeric compositions that exhibit excellent physical properties and chemical resistance. Furthermore, the cure site monomers employed in the fluoroelastomers of this invention do not adversely affect the polymerization process, nor do byproducts of the curing reaction pose an environmental concern.
The fluoroelastomers of this invention comprise copolymerized units of A) a first monomer which is a fluoroolefin selected from the group consisting of vinylidine fluoride and tetrafluoroethylene B) a second monomer, which is not the same as the first monomer, and which is selected from the group consisting of fluoroolefins, hydrocarbon olefins, perfluoro(alkyl vinyl)ethers and perfluoro(alkoxy vinyl) ethers; and C) a fluorovinyl ether cure site monomer of the formula CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFxe2x95x90CF2, wherein Rf is a C1-C8 perfluoroalkyl group or a C1-C8 perfluoroalkoxy group, n is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1 to 4.
Optionally, the fluoroelastomers of this invention may further comprise copolymerized units of at least one additional monomer, different from said first, second and cure site monomers. The additional monomer or monomers may be selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, fluoroolefins and hydrocarbon olefins.
In addition, the fluoroelastomer copolymers of this invention may optionally contain up to about 1 wt. % iodine bound to polymer chain ends, the iodine being introduced via use of an iodine-containing chain transfer agent during polymerization.
Examples of fluoroolefin monomers useful as the second monomer and as the optional additional monomer in the fluoroelastomers of this invention include, but are not limited to vinylidene fluoride (VF2), tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), pentafluoropropylene, vinyl fluoride and the like.
Hydrocarbon olefin monomers which may be employed as the second monomer and as the optional additional monomer in fluoroelastomers of this invention contain no fluorine atoms. Examples of such hydrocarbon olefins include, but are not limited to ethylene (E), propylene (P), butylene xe2x88x921 and isobutylene.
Perfluoro(alkyl vinyl) ethers suitable for use as comonomers include those of the formula
CF2xe2x95x90CFO(Rfxe2x80x2O)n(Rfxe2x80x2O)mRfxe2x80x83xe2x80x83(I)
where Rf and Rf, are different linear or branched perfluoroalkylene groups of 2-6 carbon atoms, m and n are independently 0-10, and Rf is a perfluoroalkyly group of 1-6 carbon atoms.
A preferred class of PAVE includes compositions of the formula
CF2xe2x95x90CFO(CF2CFXO)nRfxe2x80x83xe2x80x83(II)
where X is F or CF3, n is 0-5, and Rf is a perfluoroalkyl group of 1-6 carbon atoms. A most preferred class of PAVE includes those ethers wherein n is 0 or 1 and Rf contains 1-3 carbon atoms. Examples of such perfluorinated ethers include perfluoro(methyl vinyl) ether and perfluoro(propyl vinyl) ether. Other useful monomers include compounds of the formula
CF2xe2x95x90CFO[(CF2)mCF2CFZO]nRfxe2x80x83xe2x80x83(III)
where Rf is a perfluoroalkyl group having 1-6 carbon atoms
m=0 or 1, n=0-5, and Z=F or CF3.
Preferred members of this class are those in which Rf is C3F7, m=0, and n=1.
Additional perfluoro(alkyl vinyl) ether monomers include compounds of the formula
CF2xe2x95x90CFO[(CF2CFCF3O)n(CF2CF2CF2O)m(CF2)p]CxF2x+1xe2x80x83xe2x80x83(IV)
where m and n independently=1-10, p=0-3, and x=1-5.
Preferred members of this class include compounds where n=0-1, m=0-1, and x=1.
Examples of useful perfluoro(alkoxy vinyl) ethers include
CF2xe2x95x90CFOCF2CF(CF3)O(CF2O)mCnF2n+1xe2x80x83xe2x80x83(V)
where n=1-5, m=1-3, and where, preferably, n=1.
Mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl) ethers may also be used.
Specific examples of the fluoroelastomers of this invention include, but are not limited to polymers having copolymerized units of the fluorovinyl ether cure site monomers of this invention and units of VF2/HFP; VF2/HFP/TFE; VF2/PMVE; VF2/PMVE/TFE; TFE/P; TFE/P/VF2; and E/TFE/PMVE.
The cure site monomers useful in the fluoroelastomers of this invention are a class of fluorovinyl ethers having the general formula CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFxe2x95x90CF2, wherein Rf is a C1-C8 perfluoroalkyl group or a C1-C8 perfluoroalkoxy group, n is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1 to 4. Preferably Rf is xe2x80x94[OCF(CF3)CF2]xxe2x80x94, wherein x is 1 or 2; n is 1, m is 1 and p is an integer from 1 to 4. A specific example of these fluorovinyl ethers includes, but is not limited to CF3CHFCF2xe2x80x94Oxe2x80x94CH2CF2CF2xe2x80x94Oxe2x80x94CF(CF3)CF2xe2x80x94OCFxe2x95x90CF2.
These cure site monomers polymerize into the fluoroelastomer polymer chain through their vinyl group, resulting in copolymerized units having pendant CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94Oxe2x80x94 side chains. During curing, the side chains may readily dehydrofluorinate to form carbon-carbon double bonds. These sites of unsaturation then act as cure sites for crosslinking.
A particular characteristic of the cure site monomer of this invention is that it acts as an independent cure site monomer that takes part in crosslinking reactions with polyhydroxylic curing agents. That is, polymers that contain copolymerized units of this cure site monomer do not require the presence of copolymerized VF2 monomer sequences flanked by perfluoromonomers (e.g. HFP/VF2/HFP) for initiation of dehydrofluorination.
Because of the ease of hydrogen abstraction in the fluoroelastomer copolymers of this invention, the copolymers need contain only low levels of cure site monomer, i.e. 0.3-5 wt. % (preferably 0.7-3 wt. %), to promote efficient polyhydroxylic cures. This permits adjustment of other comonomer levels to maximize particular physical properties. Thus, the polymers of the present invention exhibit excellent cure characteristics when only low levels of cure site monomer are present.
The fluorovinyl ether monomers of this invention may be prepared by a process comprising the steps of a) chlorinating an hydroxy vinyl ether compound of the formula HOxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFxe2x95x90CF2 to produce a chlorinated hydroxy ether of the formula HOxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFClxe2x80x94CF2Cl; b) condensing said chlorinated hydroxy ether with hexafluoropropene to produce a chlorinated ether of the formula CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFClxe2x80x94CF2Cl; and c) dechlorinating said chlorinated ether to produce a fluorinated vinyl ether of the formula CF3CHFCF2xe2x80x94(O)nxe2x80x94(CH2)mxe2x80x94(CF2)pxe2x80x94Rfxe2x80x94OCFxe2x95x90CF2. A preferred means for dechlorinating is by reaction with a reducing agent (such as zinc) in an aprotic solvent at a temperature between 70 to 140xc2x0 C. The hydroxy vinyl ether starting material is known in the art. Some of these hydroxy vinyl ethers are available commercially from DuPont, or they may be synthesized by the process disclosed in U.S. Pat. No. 4,982,009.
In the above process, the hydroxy vinyl ether may be chlorinated by a variety of means including by the reaction with neat chlorine at a temperature between xe2x88x9215 to 40xc2x0 C., preferably 0 to 10xc2x0 C.
The chlorinated hydroxy ether may be condensed with hexafluoropropene by a variety of means, including by the reaction at a temperature between xe2x88x9215 to 70xc2x0 C. of hexafluoropropylene with the chlorinated vinyl ether contained in an anhydrous aprotic solvent and in the presence of a strong base. Suitable aprotic solvents include dimethylsufoxide and dimethylformamide. Suitable strong bases include potassium t-butoxide.
The polymers of this invention may be prepared using free radical batch or semi-batch, or continuous free radical emulsion polymerization processes. They may also be prepared by free radical suspension polymerization processes.
For example, if a continuous emulsion process is utilized, the polymers are generally prepared in a continuous stirred tank reactor. Polymerization temperatures may be in the range of 40xc2x0 to 145xc2x0 C., preferably 80xc2x0 to 135xc2x0 C. at pressures of 1 to 8 MPa. Residence times of 20 to 360 minutes are preferred. Free radical generation may be effected through use of a water-soluble initiator such as ammonium persulfate, either by thermal decomposition or by reaction with a reducing agent such as sodium sulfite. An inert surface-active agent such as ammonium perfluorooctanoate may be utilized to stabilize the dispersion, usually in conjunction with addition of a base such as sodium hydroxide or a buffer such as disodium phosphate to control pH in the range 3 to 7. Unreacted monomer is removed from the reactor effluent latex by vaporization at reduced pressure. Polymer is recovered from the stripped latex by coagulation. For example, coagulation may be effected by reducing latex pH to about 3 by addition of acid, then adding a salt solution, such as an aqueous solution of calcium nitrate, magnesium sulfate, or potassium aluminum sulfate, to the acidified latex. The polymer is separated from the serum, then washed with water and subsequently dried. After drying, the product may be cured.
Chain transfer agents may be used in the polymerization in order to control the molecular weight distribution of the resulting polymers. Examples of chain transfer agents include isopropanol; methyl ethyl ketone; ethyl acetate; diethyl malonate; isopentane; 1,3-diiodoperfluoropropane; 1,4-diiodoperfluorobutane; 1,6-diiodoperfluorohexane; 1,8-diiodoperfluorooctane; methylene iodide; trifluoromethyl iodide: perfluoro(isopropyl) iodide; and perfluoro(n-heptyl) iodide. Polymerization in the presence of iodine-containing chain transfer agents may result in a polymer with one or two iodine atoms per fluoroelastomer polymer chain, bound at the chain ends (see for example U.S. Pat. No. 4,243,770 and U.S. Pat. No. 4,361,678). Such polymers may have improved flow and processability compared to polymers made in the absence of a chain transfer agent. Generally, up to about 1 weight percent iodine chemically bound to fluoroelastomer chain ends will be incorporated into the polymer, preferably from 0.1-0.3 wt. %.
An embodiment of the present invention is a curable composition that comprises the above-described copolymers and a polyhydroxylic curing agent. The polymers of the invention are also curable with amines and amine derivatives (e.g. carbamates).
Any of the known aromatic polyhydroxylic crosslinking agents that require accelerators for satisfactory cure rates are suitable for use with the fluoroelastomers of the present invention. The crosslinking agent is usually added in amounts of from about 0.5-4 parts by weight per hundred parts by weight fluoroelastomer (phr), usually 1-2.5 phr. Preferred crosslinking agents are di- tri-, tetrahydroxybenzenes, naphthalenes, anthracenes and bisphenols of the formula 
were A is a stable divalent radical, such as a difunctional aliphatic, cycloaliphatic, or aromatic radical of 1-13 carbon atoms, or a thio, oxy, carbonyl, sulfinyl, or sulfonyl radical; A is optionally substituted with at least one chlorine or fluorine atom; x is 0 or 1; n is 1 or 2 and any aromatic ring of the polyhydroxylic compound is optionally substituted with at least one atom of chlorine, fluorine, or bromine, a xe2x80x94CHO group, or a carboxyl or acyl radical (e.g. a xe2x80x94COR where R is OH or a C1xe2x80x94C8 alkyl, aryl, or cycloalkyl group). It will be understood from the above formula describing bisphenols that the xe2x80x94OH groups can be attached in any position (other than number one) in either ring. Blends of two or more such compounds can also be used.
Referring to the bisphenol formula shown in the previous paragraph, when A is alkylene, it can be, for example, methylene, ethylene, chloroethylene, fluoroethylene, difluoroethylene, 1,3-propylene, 1,2-propylene, tetramethylene, chlorotetramethylene, fluorotetramethylene, trifluorotetramethylene, 2-methyl-1,3-propylene, 2-methyl-1,2-propylene, pentamethylene, and hexamethylene. When A is alkylidene, it can be for example ethylidene, dichloroethylidene, difluoroethylidene, propylidene, isopropylidene, trifluoloisopropylidene, hexafluoroisopropylidene, butylidene, heptachlorobutylidene, heptafluorobutylidene, pentylidene, hexylidene, and 1,1-cyclohexylidene. When A is a cycloalkylene radical, it can be for example 1,4-cyclohexylene, 2-chloro-1,4-cyclohexylene, 2-fluoro-1,4-cyclohexylene, 1,3-cyclohexylene, cyclopentylene, chlorocyclopentylene, fluorocyclopentylene, and cycloheptylene. Further, A can be an arylene radical such as m-phenylene, p-phenylene, 2-chloro-1,4-phenylene, 2-fluoro-1,4-phenylene, o-phenylene, methylphenylene, dimethylphenylene, trimethylphenylene, tetramethylphenylene, 1,4-naphthylene, 3-fluoro-1,4-naphthylene, 5-chloro-1,4-naphthylene, 1,5-naphthylene, and 2,6-naphthylene. Bisphenol AF (4,4xe2x80x2-(hexafluoroisopropylidene)diphenol) is a preferred crosslinking agent.
Other useful crosslinlking agents include hydroquinonie, dihydroxybenzenes such as catechol, resorcinol, 2-methyl resorcinol, 5-methyl resorcinol, 2-methyl hydroquinone, 2,5-dimethyl hydroquinone; 2-t-butyl hydroquinone; and 1,5-dihydroxynaphthalene.
Additional polyhydroxy curing agents include alkali metal salts of bisphenol anions, quaternary ammonium salts of bisphenol anions and quaternary phosphonium salts of bisphenol anions. For example, the salts of bisphenol A and bisphenol AF. Specific examples include the disodium salt of bisphenol AF, the dipotassium salt of bisphenol AF, the monosodium monopotassium salt of bisphenol AF and the benzyltriphenylphosphonium salt of bisphenol AF. Quaternary ammonium and phosphonium salts of bisphenol anions and their preparation are discussed in U.S. Pat. Nos. 4,957,975 and 5,648,429.
In addition, derivatized polyhydroxy compounds, such as diesters, are useful crosslinking agents. Examples of such compositions include diesters of phenols, such as the diacetate of bisphenol AF, the diacetate of sulfonyl diphenol, and the diacetate of hydroquinone.
When cured with polyhydroxy compounds, the curable compositions will also generally include a cure accelerator. The most useful accelerators are quaternary phosphonium salts, quaternary alkylammonium salts, or tertiary sulfonium salts. Particularly preferred accelerators are n-tetrabutylammonium hydrogen sulfate, tributylallylphosphonium chloride and benzyltriphenylphosphonium chloride. Other useful accelerators include those described in U.S. Pat. Nos. 5,591,804; 4,912,171; 4,882,390; 4,259,463 and 4,250,278 such as tributylbenzylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, benzyl tris(dimethylamino)phosphonium chloride; 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenonium chloride, [(C6H5)2S30(C6H13)][Cl]xe2x88x92, and [(C6H13)2S(C6H5) ]+[(CH3CO2)]xe2x88x92. In general, about 0.2 phr accelerator is an effective amount, and preferably about 0.35-1.5 phr is used.
If quaternary ammonium or phosphonium salts of bisphenols are used as curing agents, then addition of a cure accelerator is not necessary.
The polyhydroxy cure system will also contain a metal compound composed of a divalent metal oxide, such as magnesium oxide, zinc oxide, calcium oxide, or lead oxide, or a divalent metal hydroxide; or a mixture of the oxide and/or hydroxide with a metal salt of a weak acid, for example a mixture containing about 1-70 percent by weight of the metal salt. Among the useful metal salts of weak acids are barium, sodium, potassium, lead, and calcium stearates, benzoates, carbonates, oxalates, and phosphites. The amount of the metal compound added is generally about 1-15 phr, about 2-10 parts being preferred.
Other additives may be compounded into the fluoroelastomer to optimize various physical properties. Such additives include carbon black, stabilizers, plasticizers, lubricants, pigments, fillers, and processing aids typically utilized in perfluoroelastomer compounding. Any of these additives can be incorporated into the compositions of the present invention, provided the additive has adequate stability for the intended service conditions.
Carbon black is used in elastomers as a means to balance modulus, tensile strength, elongation, hardness, abrasion resistance, conductivity, and processability of the compositions. Carbon black is generally useful in amounts of from 5-60 phr.
In addition, or in the alternative, fluoropolymer fillers may be present in the composition. Generally from 1 to 50 phr of a fluoropolymer filler is used, and preferably at least about 5 phr is present. The fluoropolymer filler can be any finely divided, easily dispersed plastic fluoropolymer that is solid at the highest temperature utilized in fabrication and curing of the perfluoroelastomer composition. By solid, it is meant that the fluoroplastic, if partially crystalline, will have a crystalline melting temperature above the processing temperature(s) of the perfluoroelastomer(s). Such finely divided, easily dispersed fluoroplastics are commonly called micropowders or fluoroadditives. Micropowders are ordinarily partially crystalline polymers.
A preferred additive class includes molecular sieves, particularly zeolites. Molecular sieve zeolites are crystalline aluminosilicates of Group IA and Group IIA elements, such as sodium, potassium, magnesium, and calcium. Chemically, they are represented by the empirical formula: M2/nO.Al2O3.ySiO2.wH2O where y is 2 or greater, n is the cation valence, and w represents the water contained in the voids of the zeolite. Commercially available examples of such compositions include Molecular Sieve 3A, Molecular Sieve 4A, Molecular Sieve 5A, and Molecular Sieve 13X, all available from Aldrich Chemical Co., Inc. Milwaukee, Wis. Use of this class of additives prevents sponging and improves heat aging of vulcanizates upon press curing in many instances. In general, use of about 1-5 phr is sufficient.
Other preferred additives include modified silane coated mineral fillers. By xe2x80x9cmodified silanexe2x80x9d is meant that the silane contains at least one reactive functional group such as an amino group, or an epoxy group. The mineral fillers used in this invention are preferably somewhat alkaline, such as calcium metasilicates (CaSiO3), especially wollastonite. Wollastonite coated with either an aminosilane or an epoxysilane is especially preferred. These compounds are commercially available from Quarzwerke GmbH of Freschen, Germany as Tremin(copyright)283 EST (epoxysilane treated wollastonite) and Tremin(copyright)283 AST (aminosilane treated wollastonite). These modified silane coated mineral fillers prevent sponging of the fluoroelastomer composition during press cure and also accelerate the cure rate. Generally, about 5 to 80 phr modified silane coated mineral filler is useful in the compositions of this invention, about 10 to 60 phr being preferred.
The crosslinking agent, accelerator, metal oxide, and other additives are generally incorporated into the polymer by means of an internal mixer or on a rubber mill. The resultant composition is then cured, generally by means of heat and pressure, for example by compression transfer or injection molding.
The curable compositions of the present invention are useful in production of gaskets, tubing, seals and other molded components. Such articles are generally produced by molding a compounded formulation of the curable composition with various additives under pressure, curing the part, and then subjecting it to a post cure cycle. Depending on the monomers employed in the fluoroelastomer, the cured compositions have excellent low temperature flexibility and processability as well as excellent thermal stability and chemical resistance. They are particularly useful in applications such as seals and gaskets requiring a good combination of oil resistance, fuel resistance and low temperature flexibility, for example in fuel injection systems, fuel line connector systems and in other seals for high and low temperature automotive uses.
The invention is now illustrated by certain embodiments wherein all parts and percentages are by weight unless otherwise specified.